Heat insulating panel and method of making same



March 1, 1960 1'. A. HERBERT, JR

HEAT INSULATING PANEL AND METHOD OF MAKING SAME Filed Nov. 28, 1955 2 Sheets-Sheet 1 I Il/IIII I!!! lllIl/llllll INVENTOR. TAJIERBERT JP.

ATTORNEY March 1, 1960 "r. A. HERBERT, JR 2,926,761

HEAT INSULATING PANEL AND METHOD OF MAKING SAME Filed Nov. 28, 1955 2 Sheets-Sheet 2 IN VEN TOR.

T- A HERBER T JR.

ATTORNEY HEAT INSULATING PANEL AND NIETHOD OF MAKING SAME Thomas A. Herbert, Jr., Chula Vista, Calif., assignor to Rohr Aircraft Corporation, Chula Vista, Caiifi, a cor poration of California Application November 28, 1955, Serial No. 549,321

1 Claim. (Cl. 189-34) This invention relates to a' heat insulating panel and the method of making such panels.

The use of higher temperatures in the duct systems and power plants of airplanes, especially those using jet engines, than those formerly used has developed a demand for heat insulating panels which can be assembled together to form a heat barrier which will confine the heat within the duct or other member through which the current of hot gas is passing. It is a purpose of my invention to provide a heat insulating panel which will conduct away only a small amount of the heat even when the temperature difference between the opposite faces of the panel is over 400 F.

Another object is to provide such .a heat insulating panel which will not be damaged when subjected to temperatures of the order of 1000 to 1800 F.

A further object is to provide a panel of the type described which is light in weight and thin so that it may be installed in confined spaces in airplanes and other structures where there is insufficient room to accommodate the usual type of thick heat insulator.

Another object is to provide a panel of the type described which is made entirely of fireproof material and therefore is not a fire hazard.

A further object is to provide a panel in which in order for heat to escape, it must first pass through a plurality of thin metal cells interconnected together in the form of a honeycomb and also through a layer of fabric or matting of low thermal conductivity, the cells of the honeycomb being arranged to lend great strength and stiffness to the assembly.

- Further objects will become apparent as a description of different types of panels proceeds. For a better understanding of the invention, reference is made to the accompanying drawings, in which:

Fig. 1 is a sectional view of a portion of a heat insulating panel embodying the invention;

Fig. 2 is a bottom view of a portion of a heat-insulating fabric shown in Fig. 1;

Fig. 3 is a sectional view showing the component parts of a metal honeycomb panel assembled for brazing together;

Fig. 4 is a sectional view on line 4-4 of Fig. 3 showing one corner portion of the panel;

Fig. 5 is a view, partly diagrammatic, showing the panel of Fig. 3 in a furnace ready for brazing;

Fig. 6 is an exploded perspective view showing the parts of a modified form of insulating panel and;

Fig. 7 is a perspective view of the panel of Fig. 6 after assembly with certain parts broken away to show the interior construction.

Referring to Figs. 1 and 2, a pad 10 made of incombustible material of low thermal conductivity has a series of small holes 11 made through it every 2 inches. The pad is preferably made of quartz glass woven fabric and may be a single layer having a thickness of about .020 inch or more or the pad may have two or more such 2,926,761 Patented Mar. 1, 1960 layers depending on the amount of insulation required. The pad is placed between two rectangular sheets 12', 13 of stainless steel if a rectangular panel is to be made, otherwise the sheets 12, 13 will be cut to the desired shape. Sheets 12, 13 preferably have a thickness of from .001 to .003 inch. The sheets are preferably pressed together at each hole 11 by the electrodes of a spot welding machine and tack welded together. Or at each hole the sheets may be stitched together or secured by small staples or rivets. Sheet 12, after being cleaned, is covered with a strip 14 of brazing alloy, about .002 inch thick. For brazing to stainless steel, strip 14 is suitably made of an alloy consisting of percent silver and 15 percent manganese. On strip 14 is placed the lower end of a honeycomb core 15 having vertical cell walls 16 made of stainless steel from .001 to .003 inch thick. The cells may be of the shape shown in Fig. 4 or other desired shape. The top of core 15 is next covered with a strip 17 of brazing alloy similar to strip 14 and strip 17 covered with a stainless steel sheet 18 similar to sheet 13.

The assembly is then put in a press 19 which may be of the type shown in Fig. 5, the press comprising upper and lower rigid metal plates 2021 which may be drawn together by tightening the nuts 22 of bolts 23. Thin stainless steel peel skins 24 having a thickness of about .001 inch are preferably interposed between the panel and plates 20 and 21. The press and contained panel are placed in a furnace 25 from which the air is purged by opening a valve 26 in outlet pipe 27 and connecting inlet pipe 28 to a tank 29 of a suitable inert gas under pressure. This gas is preferably dry argon or hydrogen or a mixture of both. When the air is all out of the furnace, the furnace is heated by passing electrical current through heating resistor 30 disposed in the floor and walls of a the furnace. The panel is heated to a temperature of 1800 F. for a few minutes then the current shut off. The brazed panel is left to cool in the inert atmosphere so that no oxidation of its parts takes place which would weaken it substantially.

The sheets 12 and 18 have become securely brazed to core 15 and the high furnace temperature has not charred or otherwise injured the quartz glass fabric 10 whose fibers remain intact. In using the panel as a heat insulator or part of a heat insulating duct, it'is placed so that sheet 13 is exposedtothe high temperature while sheet 18 is exposed to the atmosphere, if possible. With a panel of the type described having a core 15 approximately /2 inch thick, there was only a small amount of heat radiated from sheet 18 when sheet 13 was kept at a temperature of about 900 F. While the panel is light in weight, its stainless steel honeycomb core makes it strong and rigid.

In making the heat-insulating panel shown in Fig. 7, channels 31 are abutted against the sides of stainless steel honeycomb core 15' (see Figs. 3 and 4) and channels 32 against the front and rear ends. The assembly is placed on a strip 33 of brazing alloy under which is a sheet 34 of stainless steel. The top of core 15' and the channels is then covered with a strip 35 of brazing alloy and a thin plate or sheet 36 of stainless steel. Tack welds may be made at spaced apart points along the edges of sheets 34 and 36 and the flanges of the channels to hold the parts together previous to brazing. The panel is then put in press 19 and brazed in the manner previously described.

Referring to Figs. 6 and 7, a plurality of copper bars 37 are laid on plate 36 and spaced 2 inches apart. Straddling each bar is a plurality of stainless steel spacers 38, each spacer having a flat top 39 and a base consisting of a pair of projecting flanges 40. The spacers are spaced 2 inches apart and their flanges 40 spot welded to plate 36. The bottom fianges 41 of a pair of channels 42 are resistance welded to the top of plate 36 along the sides thereof by a suitable electric welding machine, not shown. A thin sheet 43 of stainless steel is then laid on top of spacers 38 and a plurality of clips 44 are then laid on sheet 43 over the spacers. Each clip is composed of two leaves having pointed upper ends 45 and outwardly projecting bases 46. By connecting one end of the welding transformer secondary (not shown) to the end of a bar 37 and its other end to a spot welding electrode (not shown) and pressing the welding electrode down on the bases 46 of the clips successively, the clips are welded to sheet 43 and the sheet 43 welded to the tops 39 of the spacers 38 in contact with that bar 37. The transformer secondary is now connected to the next bar 37 and the clips 44 above this bar spot welded to sheet 43 and this sheet to the spacers 38. This process is continued until all the clips have been secured to sheet 43. The use of a heavy metal bar against which thin metal parts to be spot welded together are pressed by a welding electrodeis shown in Fig. 4 of US. Patent No. 2,599,045. A pad 47 of soft heat insulating material is now pressed down against the clips 44 until their pointed ends 45 penetrate the pad and the pad rests on sheet 43. The

size of pad 47 is somewhat less than that of sheet 43, so that the edges of sheet 43 extend out slightly beyond those of the pad, as shown. The pad illustrated is made of a piece of quartz glass woven fabric but it may be made of a thin layer of such fabric covered by a thicker layer of quartz fibers lightly pressed together to form a light, porous matting. Or the entire pad could be a light matting of quartz glass fibers or asbestos fibers. The ends 45 of the clips are next spread apart and bent down against the pad, as shown in Fig. 7, thus securing the pad to sheet 43. A thin stainless steel sheet 48 the same size as sheet 43 is now placed on top of the pad and spot welded to the bent over ends of clips 44 by pressing a welding electrode down against the top of sheet 48 directly above the clips. During this welding the copper bars 37 act as supports and also carry the welding current, as above described.

The bars 37 are now withdrawn by sliding them endwise through spacers 38 and a pair of end channels 49, 50 secured to the top of sheet 36 by resistance welding their outwardly projecting lower flanges 51 to the sheet. The channels 42, 49 and 50 are high enough that their upper flanges touch the bottom face of sheet 43 along the edges thereof thus providing a dead air space between the top plate 36 of the honeycomb panel and the metal envelope containing the quartz glass insulation. By making the honeycomb panel of the materials described and sheets 43 and 48 of stainless steel from .001 to .003 inch thick, a heat insulating panel is secured which will conduct away only a little heat when its top face is exposed to a temperature of about 1000" F. Furthermore the panel is strong yet so light in weight that it may be used around ducts and other parts of airplanes subjected to high temperatures without appreciably increasing the weight of the plane.

if an additional layer of insulation is required, another set of clips (not shown) may be attached to the top of sheet 43 and a second insulating pad similar to pad 47 to the top of sheet 48 by bending down the tops h clips in the manner above described.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment of the invention is therefore to be considered as in all r spects iilustrative and not restrictive, the scope the invention being indicated by the appended claim, and all changes which come within the meaning and range of equivalency of the claim are intended to be embraced therein.

Have thus described my invention, what I claim as new and useful and desire-to secure by Letters Patent is:

A li htweight heat insulating panel capable of withstanding at temperature of the order of 1800 F. for a prolonged period, comprising two imperforate stainless steel sheets each having a thickness of the order of from .001 to .003 inch; a soft compressible pad composed of incombustihle heat insulating material having low thermal conductivity, said pad being disposed between said sheets and having a thickness or" the order of upwards of .020 inch, said pad having a plurality of small spaced apart holes therein and said sheets being welded together within the area of said holes and said pad being compressed around the area of said holes; a stainless steel core composed of a plurality of interconnected honeycomb cells, the wall of each cell being solid metal of a thickness of from .001 to .003 inch; a continuous mass of metal brazalloy connecting one end of each of said cells to the exposed face of one of said sheets; a stainless steel imperforate sheet having a thickness of from .001 to .003 inch; and a continuous mass of metal brazing alloy connecting said last named sheet to each of said cells at the opposite end thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,001,632 Schlichting May 14, 1935 2,319,455 Hardman et al. May 18, 1943 2,778,458 Briggs Jan. 22, 1957 

